Descents, head or feet down first??

jdz · 15th August 2005, 02:20

As some already know, I dive a Prism and I generally have no probs at rapid head down descents, however I have been caught on a number of occasions where the air/gas in my unit has been "forced" out of my clungs and into the scrubber part of the loop, effectively starving me of any gas to inhale!!

If my hands aren't free, which can usually be the case.. reel, torch, carry bag or holding the shot... and suddenly going for the "ADV" button to inject is a real PITA!!

As I haven't dived other units (except LARs & Dolphins) I was curious to know if this is a regular occurance with over the shoulder clung systems??

Cheers, JDZ

Underwaterbear · 15th August 2005, 03:23

John,

It sounds like what you are experiencing is just the result of a fast decent and the ADV not being very "automatic". I doubt the attitude of decent has anything to do with it, other than making the CLs bottom out earlier. You need to check that the two short lengths of webbing on the CL adjacent the ADV are folding out when the CL collapses. I found that if I did not fix it early, one side (usually the inside - that is closest to centre) collapses partially underneath the ADV, stopping the ADV from "landing" squarely on the activating button inside the CL.

Does this make sense in your scenario?

Cheers

**Steve** · 15th August 2005, 03:24

Am I understanding you correctly John? Is your ADV not keeping up with your descent speed? There is nothing special about OTS lung units ADV operation it is purely a product of loop volume, so if I’m reading you correctly it sounds as though your ADV isn’t providing enough gas. Is this right?

Chris · 15th August 2005, 03:37

Yep mine is the same as Bears.
If I don't get the two bits of webbing on the counterlung lined up so they flex out together as the lung collapses the ADV does not drop on centre and will not fire.

I tend to pull the bits of webbing outward from the counterlung just before decent this seems to keep it the ADV lined up pretty well.

Steve What sort of condition is the PRISM in that’s for sale in WA?
What is Red Dog doing today?

Cheers
Chris

jdz · 15th August 2005, 03:41

Yes the clung collapses as I invert, and maybe the clung is not does not "fold correctly" but it certainly does not inflate when I inhale and the clung has definitely collapsed, that is bottomed out!
I need to grap the valve and squeeze to get a breath in!
Cheers, JDZ

**Steve** · 15th August 2005, 03:46

Bloody PRISMs

How tight have you got your CLs pulled down? Given you can make the schrader fire manually it sounds like a placement issue rather than a component one. Should be a easy enough fix for you.

Red Dog modified my wetsuit on the weekend :-(

wizbang · 15th August 2005, 03:50

For those reading on that don't know, the prism ADV is like a 2nd stage reg without the bezel. In otherwords the lever of the 2nd stage is depressed by the bottom side of the CL, (that side against the divers chest) when the lung bottoms out because there isn't enough gas in the loop.

This is as apposed to an Inspo or Dolphin ADV which uses the negative presure and a diaphram to work the lever. (I am not sure about other rebreather ADV's).

JDZ I would agree that it sounds like the ADV isn't activating because it can't bottom out. I haven't had the problem on either a KISS, Inspo or Dolphin. (some were harder to activate than others but still I didn't need to activate the ADV manually, even if I could reach.)

We haven't dived together enough yet, but as Mike will atest to, my full name is Mr Wizbang Stone.

Rich Sawkins · 15th August 2005, 04:10

John, I get similar issues if the ADV isn't correctly positioned, especially on fast decents (feet first, I rarely do head first).

I like to check it at 5m when doing a bubble check and make sure I've got it positioned correctly as mentioned by the guys above. I find that decending more slowly the problem rarely appears.

Cheers
Rich

Mike · 15th August 2005, 07:06

Quote: (Originally Posted by wizbang)

We haven't dived together enough yet, but as Mike will atest to, my full name is Mr Wizbang Stone.

I thought that was the derivation of your name? The Wizzz as you went past, and the Bang as you hit bottom?
I averaged 25m per minute descent on that dive, and Wiz started after me, and was tying off the anchor by the time I got down.

I find you have to sort the ADV out before you run out of volume - you actually need a bit of volume to be able to align the adv with the striker plate so that it works. If you suck a vacuum on the lung, it is very hard to be able to align the adv so that you can get any volume through it. OTOH, when the ADV is aligned it seems to work quite easily. I have two descents which stop halfway down, ascend slightly, then descend again when I decided that loop volume was a good thing.

One think I've considered is the sternum strap - I habitually neglect to do it up and suspect that having it tensioned may help lay the lung out better, and hence help the ADV to work?

I'm curious about what's down there, so definately head first, but if anything it should make the ADV fire earlier as the ADV is then at the lowest point of the loop, hence collapses first and fires the ADV.

Mike
edit: up? down? I dunno...

silent running · 16th August 2005, 02:36

Hello all, as an owner of an older model Prism, I don't have the webbing on the outside side of the CL like the newer models. I have never had a problem with the ADV on descents. I think there is a connection. I'm thinking the webbing makes the lung just a bit too stiff to collapse all the way, which keeps the schrader valve ADV from depressing. Doesn't the Meg also have a similar system? Their CLs seem to be even stiffer material, I wonder if fast descents are ever a problem for Meg owners due to their stiffness?

15th August 2005, 02:20	#1 (permalink)
jdz Prism Cave Diver Current Rebreather/s: Prism Topaz Dolphin Home Build Other Rebreather/s: Dolphin Home Build Join Date: Feb 2005 Location: Melbourne Australia Posts: 217	Descents, head or feet down first?? As some already know, I dive a Prism and I generally have no probs at rapid head down descents, however I have been caught on a number of occasions where the air/gas in my unit has been "forced" out of my clungs and into the scrubber part of the loop, effectively starving me of any gas to inhale!! If my hands aren't free, which can usually be the case.. reel, torch, carry bag or holding the shot... and suddenly going for the "ADV" button to inject is a real PITA!! As I haven't dived other units (except LARs & Dolphins) I was curious to know if this is a regular occurance with over the shoulder clung systems?? Cheers, JDZ
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15th August 2005, 03:23	#2 (permalink)
Underwaterbear A Prismer in Megland Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: May 2005 Location: Seattle, WA Posts: 185	John, It sounds like what you are experiencing is just the result of a fast decent and the ADV not being very "automatic". I doubt the attitude of decent has anything to do with it, other than making the CLs bottom out earlier. You need to check that the two short lengths of webbing on the CL adjacent the ADV are folding out when the CL collapses. I found that if I did not fix it early, one side (usually the inside - that is closest to centre) collapses partially underneath the ADV, stopping the ADV from "landing" squarely on the activating button inside the CL. Does this make sense in your scenario? Cheers
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15th August 2005, 03:24	#3 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,100	Am I understanding you correctly John? Is your ADV not keeping up with your descent speed? There is nothing special about OTS lung units ADV operation it is purely a product of loop volume, so if I’m reading you correctly it sounds as though your ADV isn’t providing enough gas. Is this right? __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types.
(Online)

15th August 2005, 03:37	#4 (permalink)
Chris Go Nude Or Go Home Current Rebreather/s: Megalodon Other Rebreather/s: Inspiration Classic Megalodon Prism Topaz Sport Kiss Join Date: Feb 2005 Location: Perth, Western Australia Posts: 607	Yep mine is the same as Bears. If I don't get the two bits of webbing on the counterlung lined up so they flex out together as the lung collapses the ADV does not drop on centre and will not fire. I tend to pull the bits of webbing outward from the counterlung just before decent this seems to keep it the ADV lined up pretty well. Steve What sort of condition is the PRISM in that’s for sale in WA? What is Red Dog doing today? Cheers Chris __________________ Megalodon Sorb and Sensors whilst in Australia www.divetub.com.au Diving & Photography @ www.uwphotog.com
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15th August 2005, 03:41	#5 (permalink)
jdz Prism Cave Diver Current Rebreather/s: Prism Topaz Dolphin Home Build Other Rebreather/s: Dolphin Home Build Join Date: Feb 2005 Location: Melbourne Australia Posts: 217	Yes the clung collapses as I invert, and maybe the clung is not does not "fold correctly" but it certainly does not inflate when I inhale and the clung has definitely collapsed, that is bottomed out! I need to grap the valve and squeeze to get a breath in! Cheers, JDZ
(Offline)

15th August 2005, 03:46	#6 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,100	Bloody PRISMs How tight have you got your CLs pulled down? Given you can make the schrader fire manually it sounds like a placement issue rather than a component one. Should be a easy enough fix for you. Red Dog modified my wetsuit on the weekend :-( __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types.
(Online)

15th August 2005, 03:50	#7 (permalink)
wizbang WEB MERMEN Current Rebreather/s: Inspiration Classic Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Vision Evolution Prism Topaz Sport Kiss Classic Kiss Dolphin Home Build Join Date: Feb 2005 Location: Perth Australia Posts: 385	For those reading on that don't know, the prism ADV is like a 2nd stage reg without the bezel. In otherwords the lever of the 2nd stage is depressed by the bottom side of the CL, (that side against the divers chest) when the lung bottoms out because there isn't enough gas in the loop. This is as apposed to an Inspo or Dolphin ADV which uses the negative presure and a diaphram to work the lever. (I am not sure about other rebreather ADV's). JDZ I would agree that it sounds like the ADV isn't activating because it can't bottom out. I haven't had the problem on either a KISS, Inspo or Dolphin. (some were harder to activate than others but still I didn't need to activate the ADV manually, even if I could reach.) We haven't dived together enough yet, but as Mike will atest to, my full name is Mr Wizbang Stone.
(Offline)

15th August 2005, 04:10	#8 (permalink)
Rich Sawkins New Member Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Feb 2005 Location: Sydney, Australia Posts: 74	John, I get similar issues if the ADV isn't correctly positioned, especially on fast decents (feet first, I rarely do head first). I like to check it at 5m when doing a bubble check and make sure I've got it positioned correctly as mentioned by the guys above. I find that decending more slowly the problem rarely appears. Cheers Rich
(Offline)

15th August 2005, 07:06	#9 (permalink)
Mike Prism 'prentice Current Rebreather/s: Prism Topaz Other Rebreather/s: Inspiration Classic Evolution Join Date: Feb 2005 Location: Melbourne Posts: 327	Quote: (Originally Posted by wizbang) We haven't dived together enough yet, but as Mike will atest to, my full name is Mr Wizbang Stone. I thought that was the derivation of your name? The Wizzz as you went past, and the Bang as you hit bottom? I averaged 25m per minute descent on that dive, and Wiz started after me, and was tying off the anchor by the time I got down. I find you have to sort the ADV out before you run out of volume - you actually need a bit of volume to be able to align the adv with the striker plate so that it works. If you suck a vacuum on the lung, it is very hard to be able to align the adv so that you can get any volume through it. OTOH, when the ADV is aligned it seems to work quite easily. I have two descents which stop halfway down, ascend slightly, then descend again when I decided that loop volume was a good thing. One think I've considered is the sternum strap - I habitually neglect to do it up and suspect that having it tensioned may help lay the lung out better, and hence help the ADV to work? I'm curious about what's down there, so definately head first, but if anything it should make the ADV fire earlier as the ADV is then at the lowest point of the loop, hence collapses first and fires the ADV. Mike edit: up? down? I dunno...
(Offline)

16th August 2005, 02:36	#10 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,814	Hello all, as an owner of an older model Prism, I don't have the webbing on the outside side of the CL like the newer models. I have never had a problem with the ADV on descents. I think there is a connection. I'm thinking the webbing makes the lung just a bit too stiff to collapse all the way, which keeps the schrader valve ADV from depressing. Doesn't the Meg also have a similar system? Their CLs seem to be even stiffer material, I wonder if fast descents are ever a problem for Meg owners due to their stiffness?
(Offline)

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